Our Liviiif; Ri'soiiives — Global Climatf Chaiijie 



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(5.4°F), 1% to 11% of 15.148 native vascular 

 plant species in North America (about 1.060 to 

 1 .670 species) could be entirely out of their cli- 

 mate envelopes. These species would thus be 

 vulnerable to extinction unless they can migrate 

 rapidly enough or can persist despite climate 

 change. In comparison, about 90 plant species 

 in North America are believed to have gone 

 extinct in the last two centuries (Russell and 

 Morse 1992). 



Rarity and Vulnerability 



Of the native vascular plant species studied, 

 about 4.100 (27%) are considered rare by The 

 Nature Conservancy {see article by Stein et al.. 

 p. .^99. for definitions of ranking system for rar- 

 ity). These species occur at fewer than 100 sites 

 or are comparably vulnerable. Our analysis 

 shows that these rare plants are likely to be fur- 

 ther affected by climate change. In this analysis, 

 about 10%- 18% of the rare species would be 

 vulnerable to a mean 3°C (5.4°F) temperature 

 increase. In contrast, only 1 % to 2% of the com- 

 mon species appear vulnerable under these con- 

 ditions. These results imply that numerous rare 

 vascular plant species could be additionally 

 threatened by climate change. Early warnings 

 of species" vulnerability to a rapidly changing 

 climate might allow the development and 

 implementation of new conservation strategies 

 before a crisis occurs, thus improving the suc- 

 cess rate for the protection of rare plants while 

 minimizing the cost. 



Regional Patterns of 

 Vulnerability 



Based on the uniform 3°C (5.4°F) mean 

 increase in temperature used for this prelimi- 

 nary climate change impacts analysis, there 

 appear to be regional patterns to the proportion 

 of potentially vulnerable species in each state or 

 province (Fig. 2). In this initially simplified 

 analysis, the southeastern states have the high- 

 est percentage of species out of their climate 

 envelopes, while the Great Plains states and 

 provinces may experience proportionally fewer 

 species losses. The relatively high proportion of 

 species vulnerability in the Southeast may be 

 due in part to the presence in state floras of 

 Appalachian Mountain species at their southern 

 range limits. Many of these species are already 

 rare in states along their southern range limits 

 and are likely to be lost from the local floras if 

 the climate warms. 



Global warming models, however, suggest 

 that the temperature and precipitation changes 

 in the interior of the continent will be far greater 

 than in coastal regions. In the Great Plains, 

 some models suggest increases in summer tem- 



Proportion of 

 state/province's ?,! 

 flora 



■ >10% 



■ 5.1 - 10% 



□ 1.1-5% 



□ 0.1 - 1% 



□ 0% 



□ Incomplete 

 data 



peratures by 4-7°C (7.2-12.6°F). accompanied 

 by dramatic decreases in precipitation. Future 

 analyses that incorporate regional changes in 

 climate projected by models will further refine 

 our understanding of regional patterns of plant 

 species" vulnerability to climate change. 



Dispersal and Persistence of 

 Vascular Plants 



The survival of species during periods of 

 changing climate will be determined in part by 

 their abilities to disperse to new sites or to per- 

 sist in place. For this analysis, a dispersal-abili- 

 ty .scale was used to assess the potential for dif- 

 ferent species to migrate. The scale is based on 

 characteristics important to species mobility 

 such as pollination mechanisms, dispersal 

 mechanisms, reproductive characteristics, 

 degree of self-compatibility, growth form, 

 trophic type, and number of populations. 

 Biological factors likely to increase species 

 mobility include wind pollination, at least par- 

 tial self-compatibility, dispersal of propagules 

 by wind or birds, and a short generation time. 

 Characteristics such as dependence on specific 

 pollinators (e.g., yucca and yucca moth), dis- 

 persal by ants, or a long generation time reduce 

 the chances for successful rapid dispersal and 

 establishment. By using these criteria, most of 

 the species studied appear to have an intermedi- 

 ate dispersal potential. 



The species in this analysis that would be 

 vulnerable in a -i-3°C (5.4°F) climate appear to 

 have characteristics that limit long-distance dis- 

 persal (Fig. 3). This suggests that the plants 

 potentially most vulnerable to climate change 

 may be those forced to adapt in place to new 

 conditions. In general, rare plants and narrow 

 endemics will be particularly endangered by 

 climate change. These plants often have restrict- 

 ed ranges, a reduced seed source, and may 

 depend on specific microclimatic conditions for 



Fig. 2. The proportion of species 

 that would be out of their climate 

 envelope in each state or province 

 with a +3°C (+5.4''F) temperature 

 change. 



